US20090301069A1

US20090301069A1 - Exhaust Gas Cleaning Component for Cleaning an Internal Combustion Engine Exhaust Gas

Info

Publication number: US20090301069A1
Application number: US12/067,105
Authority: US
Inventors: Clemens Brinkmeier; Christof Schoen; Guido Vent
Original assignee: Daimler AG
Current assignee: DAMILER AG; Mercedes Benz Group AG
Priority date: 2005-09-17
Filing date: 2006-08-26
Publication date: 2009-12-10
Also published as: EP1924340A1; WO2007031190A1; DE102005044545A1; JP2009508049A

Abstract

A component for cleaning the exhaust gas in an internal combustion engine has a carrier body with a plurality of flow ducts for the exhaust gas. At least some of the walls (3) of the flow ducts have a coating with an oxygen storage capacity. According to the invention, the coating with an oxygen storage capacity is provided for a first delimited region of the carrier body, while a second delimited region of the carrier body is made free of a coating with an oxygen storage capacity or has a coating with a greatly reduced oxygen storage capacity compared to the first region.

Description

This application is a National Stage of PCT International Application No. PCT/EP2006/008383, filed Aug. 26, 2006, which claims priority under 35 U.S.C. §119 to German Patent Application No. 102005044545.4, filed Aug. 17, 2005, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a component for cleaning the exhaust gas in an internal combustion engine.
In order to clean the exhaust gases of an internal combustion engines it is generally customary to provide, in the exhaust section, a cylindrical carrier body with a plurality of flow ducts through which the exhaust gases flow. For catalytically assisted cleaning of exhaust gas, a catalytically active coating is usually applied to the ducts, so that the exhaust gas which flows through them comes into contact with the coating and exhaust gas components catalyzed by the coating. The coatings frequently have an oxygen storage capacity, which permits, in particular, catalyzation of redox reactions.
Stressing due to elevated temperatures, however, can cause the exhaust gas cleaning component to age, reducing its functional capability. In an exhaust gas cleaning component having a coating with an oxygen storage capacity, the aging can be accompanied by a reduction in the oxygen storage function, reducing the reliability of the exhaust gas cleaning component.
One object of the invention is therefore to provide an improved exhaust gas cleaning component with improved operational reliability.
This and other objects and advantages are achieved by the exhaust gas cleaning component according to the invention, in which the coating with an oxygen storage capacity is provided for a first delimited region of the carrier body, and a second delimited region of the carrier body is made free of a coating with an oxygen storage capacity or has a coating with a greatly reduced oxygen storage capacity compared to the first region.
Preferably the coating is the type referred to as a washcoat. Depending on the intended function, it can contain finely distributed, catalytically active noble metals (particularly of the platinum group). If the coating has an oxygen storage capacity, it contains a material which is capable of storing oxygen, such as for example an oxide of an element of the rare earths. The material is distributed homogeneously in the coating or the washcoat, so that the coating has an overall oxygen storage capacity. Cerium oxide-based oxides and/or praseodymium oxide-based oxides or mixed oxides are particularly preferred as materials with an oxygen storage capacity which are distributed homogeneously in the coating so that the coating has an overall oxygen storage capacity.
For the first region, a proportion of approximately 20% to 70% of the material with an oxygen storage capacity is preferred in the coating. In contrast, for the second region a content of less than 10% is preferred. The second region can, however, also have a coating which does not contain any such material at all or it can be made completely free of a coating. For the sake of simplification, the embodiments of the first and second regions are referred to below as being an OSC-rich region and an OSC-poor or OSC-free region (OSC=oxygen storage capacity).
In an embodiment according to the invention in which only a delimited region of the carrier body is provided with an OSC-rich coating, the chemical conversions that occur by means of the material with an oxygen storage capacity are mainly or completely limited to this region of the exhaust gas cleaning component. As a result, the release of heat which is associated with the conversions is also limited to region, so that the temperature loading of the exhaust gas cleaning component is reduced, at least in the other regions. Since the oxygen storage capacity can decrease due to aging, recording or estimating the degree of aging of the exhaust gas cleaning component is also made possible by recording the oxygen storage capacity in the OSC-rich region. If excessive aging (or aging which is occurring too quickly) is detected, it is possible to intervene in the operation of the internal combustion engine to counteract. As a result, the service life and the operational reliability of the exhaust gas cleaning component are also increased.
Depending on the application, different, shaped regions of the exhaust gas cleaning component can be embodied as first and second regions. For example, the first and/or the second region can extend over the entire length of the carrier body, but not over the entire cross-sectional area. The first and/or second regions can, however, also extend over the entire cross-sectional area of the carrier body, but not over its entire length.
In one embodiment of the invention, the first region and/or the second region extend over the entire cross section of the carrier body and are limited in the axial direction with respect to the extent of the carrier body. This embodiment is particularly easy to produce by means of immersion/suction coating.
In a further refinement of the invention, the first region adjoins the second region. In particular there is provision for an OSC-rich region to extend over the entire cross section of the carrier body and to directly adjoin, in the axial direction, an OSC-poor or OSC-free region which also extends over the entire cross section. In this way, the junctions are defined unambiguously and are localized in the axial direction on the carrier body.
In a further refinement of the invention, the first (OSC-rich) region extends over the greater part of the length of the carrier body. This embodiment is advantageous in particular for exhaust gas cleaning components which require a large oxygen storage capacity in terms of absolute value for their function. This is the case, for example, in three-way catalytic converters.
In a further refinement of the invention, the first (OSC-rich) section extends from a point which is spaced apart from the inlet end of the carrier body in the axial direction to the outlet end of the carrier body. An inlet-end (preferably disk-shaped) section of the carrier body is therefore made OSC-poor or OSC-free. This prevents materials which store oxygen from experiencing increased aging in the inlet region of the exhaust gas cleaning component (which is usually particularly subject to temperature stresses). In addition, heat-supplying reactions which occur by means of the material which stores oxygen are moved axially rearward from the inlet region. On the other hand, downstream of the OSC-poor or OSC-free inlet region there is still sufficient oxygen storage capacity available for the function of the exhaust gas cleaning component.
In a further refinement of the invention, at least two first (OSC-rich) regions which are spaced apart from one another are provided for the exhaust gas cleaning component. It may, in particular, be advantageous for the functioning of an exhaust gas catalytic converter as an exhaust gas cleaning component if preferably respectively disk-shaped OSC-poor or OSC-free regions and OSC-rich regions follow one another in the axial direction, in a repeatedly alternating fashion.
In a further refinement of the invention, the exhaust gas cleaning component comprises an exhaust gas catalytic converter. The catalytic converter here may be either an unsupported or a supported catalytic converter. One embodiment of the exhaust gas cleaning component according to the invention is particularly advantageously as a three-way catalytic converter.
In a further refinement of the invention, the exhaust gas cleaning component is comprises an exhaust gas particle filter, preferably with a so-called wall flow design. The ducts of the particle filter can be catalytically coated here along their gas inlet side and/or their gas outlet side, or may be essentially free of a catalytic coating.
In a further refinement of the invention, temperature recording devices are provided for recording the temperature of the coating with an oxygen storage capacity in the first region. In this way it is possible to record changes in temperature which are caused by redox reactions which occur by means of the OSC-rich coating. If, due to aging, the activity of the coating decreases, that can be detected by reference to the recorded temperatures of the coating. In particular, by recording the temperature of the coating it is possible to detect a change in the modification process of the material which stores oxygen. (Such change occurs when oxygen is stored, since the change is usually accompanied by a heat tone.) The oxygen storage capacity of the coating with an oxygen storage capacity can therefore be recorded by means of the recorded temperature of said coating. This makes it possible to diagnose the exhaust gas cleaning component since aging-induced degradation of the function of the coating which stores oxygen can be detected by recording the temperature.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of the exhaust gas cleaning component according to the invention;

FIG. 2 shows a second embodiment of the exhaust gas cleaning component according to the invention;

FIG. 3 shows a third embodiment of the exhaust gas cleaning component according to the invention;

FIG. 4 shows a fourth embodiment of the exhaust gas cleaning component according to the invention;

FIG. 5 shows a fifth embodiment of the exhaust gas cleaning component according to the invention;

FIG. 6 shows a side view of a first arrangement of a temperature sensor for the exhaust gas cleaning component according to the invention;

FIG. 7 shows a side view of a second arrangement of a temperature sensor for the exhaust gas cleaning component according to the invention;

FIGS. 8 a to 8 d show further advantageous embodiments of the exhaust gas cleaning component according to the invention in conjunction with a temperature sensor which is arranged according to FIG. 6; and

FIGS. 9 a to 9 c show further advantageous embodiments of the exhaust gas cleaning component according to the invention in conjunction with a temperature sensor which is arranged according to FIG. 7.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exhaust gas cleaning component 1 which comprises an exhaust gas catalytic converter with a honeycomb body design. Although the exhaust gas catalytic converter 1 can be embodied as an unsupported catalytic converter, in which the honeycomb body itself is composed of catalytically active material, it is assumed below that there is a supported exhaust gas catalytic converter with a metallic or ceramic carrier body. A plurality of flow ducts 2, on at least part of whose walls 3 a (preferably a catalytically active) coating is applied (not illustrated in more detail), pass through the carrier body. In its rear region 5 (relative to the direction of flow of the exhaust gas which is indicated by the arrow 4) the exhaust gas catalytic converter 1 has an OSC-rich coating (a coating with a comparatively large oxygen storage capacity). On the other hand, in the comparatively significantly shorter inlet-end region 6, the exhaust gas catalytic converter 1 is made OSC-free or OSC-poor. That is, it can be made free of coating, or can have a coating with comparatively little or no oxygen storage capacity. For reasons of production technology it is preferred if coatings are applied approximately uniformly on the walls 3 of the flow ducts 2 in the respective regions 5, 6 and comprise the entire cross section of the exhaust gas catalytic converter 1.
The embodiment in FIG. 1, which is used near to the engine as a first catalytic exhaust gas cleaning component in the exhaust section of an internal combustion engine, is preferred. Such exhaust gas cleaning components are subjected, particularly in their inlet region, to high thermal stresses since the exhaust gas which enters can be at high temperatures. Reactions of reactive exhaust gas components with oxygen stored in the catalytic converter and/or changes in the modification process of the oxygen storage material itself can further increase the temperature stress on the catalytic converter. In order to protect the inlet-end region (which is important for the exhaust gas cleaning performance) against excessively high temperatures it may therefore be advantageous if the inlet region of the catalytic converter is made OSC-poor or OSC-free. An inlet-end region 6 of the exhaust gas catalytic converter 1 which is made OSC-poor or OSC-free over approximately 5 mm to 50 mm, or over approximately 5% to 50%, of its overall length is advantageous. The directly adjoining, downstream region 5 is preferably made uniformly OSC-rich.
FIG. 2 shows a second advantageous embodiment of an exhaust gas cleaning component 1 which is embodied according to the invention. In contrast to the embodiment in FIG. 1, an inlet-end region 5 here is OSC-rich, and a directly adjoining, downstream region 6 is made OSC-poor or OSC-free. This embodiment is recommended if an increased oxygen storage capacity is not necessary for functioning of the exhaust gas cleaning component 1. This may be done, for example, in an exhaust gas cleaning component 1 which is embodied as an oxidation catalytic converter or as a soot filter. The inlet-end OSC-rich region 5 can serve, in particular in this case, as a diagnostic region in such a way that the aging of the exhaust gas cleaning component 1 is determined by repeated determinations of the oxygen storage capacity of the OSC-rich region 5. An inlet-end region 5 of the exhaust gas cleaning component 1 which is made OSC-rich over approximately 5 mm to 50 mm, or over approximately 5% to 50%, of its overall length is advantageous.
FIG. 3 shows a third advantageous embodiment of an exhaust gas catalytic converter 1 which is embodied according to the invention. In contrast to the embodiment in FIG. 1, an inlet-end region 5′ is made OSC-rich, as is a rear region 5; that is, such regions are embodied with a coating having comparatively high oxygen storage capacity. A central region 6 which is made OSC-poor or OSC-free is arranged between the OSC-rich regions 5′, 5. The central region 6 which is made OSC-poor or OSC-free preferably makes up approximately 20% to 30% of the total length of the exhaust gas catalytic converter 1. The exhaust gas catalytic converter 1 therefore has an OSC-rich coating over the greater part of its length so that its most important function is available to a significant degree.
FIG. 4 illustrates a further advantageous embodiment of an exhaust gas catalytic converter 1. In this embodiment, only a central region 5 is made OSC-rich. On the other hand, a directly adjoining, front region 6 and a directly adjoining rear region 6′ are made OSC-poor or OSC-free. Such an embodiment is advantageous, in particular, for catalytic exhaust gas cleaning components in which a comparatively small oxygen storage capacity is necessary. Compared to a coating which is embodied with a uniformly reduced oxygen storage capacity over the entire length, this embodiment is advantageous in that only one region has a reduced temperature resistance. The central region 5 preferably makes up approximately 20% to 60% of the total length of the exhaust gas catalytic converter 1.
In the further advantageous embodiment which is illustrated in FIG. 5, OSC- rich regions 5, 5′, 5″, 5′″ alternate with OSC-poor or OSC- free regions 6, 6′, 6″, 6′″. Here, it is possible, as illustrated, for the inlet-end region 6 to be made OSC-poor or OSC-free. However, it may also be advantageous if the inlet region has a coating with a high oxygen storage capacity. Since in particular cerium-containing coatings can catalyze water vapor shift reactions with the formation of hydrogen it is possible in such a case to use hydrogen which is formed in the regions with a high oxygen storage capacity in the subsequent regions with a low oxygen storage capacity or with no oxygen storage capacity. In this way it is possible to extend the catalytic function of the exhaust gas catalytic converter 1. Each region preferably makes up approximately 20% of the total length of the exhaust gas catalytic converter 1. The individual regions may be made approximately of equal length or with different lengths.
The inventive embodiment of an exhaust gas cleaning component with a first delimited region with OSC-rich coating and a second delimited region which is made OSC-poor or OSC-free results in an improved catalytic function of the exhaust gas cleaning component. Furthermore, the embodiment according to the invention can be used to monitor aging of the exhaust gas cleaning component. For this purpose, the temperature of the coating with an oxygen storage capacity is recorded in the OSC-rich region in such a way that reaction heat of a change in the modification process of the material with an oxygen storage capacity which occurs when oxygen is stored can be recorded. When oxygen is stored in the material with an oxygen storage capacity, the material changes from an oxygen-poor modification into an oxygen-rich modification. For example, in the case of cerium oxide-based materials with an oxygen storage capacity, cerium oxide changes from its three-value form (Ce2O3) into the four-value form (CeO2). The corresponding oxygen absorbing reaction takes place very quickly in an exothermal fashion, the temperature of the coating with an oxygen storage capacity increases when oxygen is stored. The nature of the temperature increase can therefore determine whether and to what extent a change in the modification process has occurred, i.e. whether and to what extent material with an oxygen storage capacity is available. Since aging of a catalytic converter due, for example, to the effect of increased temperatures or of poisoning, becomes apparent through a reduction in the oxygen storage capacity, it is possible, by evaluating the increase in temperature when oxygen is stored, to assess the state of aging of the exhaust gas cleaning component and carry out diagnostics. For this purpose, for example the magnitude of the increase in temperature is detected and compared with a reference value.
The nature and the effect of the increase in temperature which occurs when oxygen is stored in the material with an oxygen storage capacity must be clearly differentiated here from increases in temperature which may occur due to the occurrence of catalyzed gas reactions. While, in the case mentioned first, an exothermal change in the modification process in the material with an oxygen storage capacity is the cause of the increase in temperature, in the case mentioned second that cause is exothermal reactions of exhaust gas components. The reaction heat which is released with the storage of oxygen therefore acts directly in the coating itself and as a result heats it up very quickly, causing an increase in temperature, even if no exothermal gas reactions occur.
In contrast, gas reactions which are catalyzed by the coating heat up the coating indirectly and occur after a delay, in particular in regions of the exhaust gas cleaning component which are at a distance from the gas inlet. Consequently, when temperature is recorded at a distance from the exhaust gas inlet, it is possible to differentiate between the temperature-increasing effect of a gas oxidation and a change in the modification process in the coating. This means that when temperature is recorded at a distance from the exhaust gas inlet, it is possible to monitor the exhaust gas cleaning component particularly reliably by determining the oxygen storage capacity which is present there. An increase in temperature which occurs immediately when there is a change of operating mode of the internal combustion engine with a changeover from reducing exhaust gas conditions with a deficit of oxygen to oxidizing exhaust gas conditions with an excess of oxygen is preferably evaluated. In this way it is possible to effectively eliminate temperature effects which are caused by gas oxidations.
The reaction heat of the change in the modification process which occurs when oxygen is stored in the material with an oxygen storage capacity can advantageously be recorded with exhaust gas cleaning components which are predominantly provided from the outset, with an OSC-rich coating corresponding to the embodiments illustrated in FIGS. 1 and 3. The temperature can be recorded at a single point in the OSC-rich coating or at a plurality of points which are offset with respect to one another axially and/or radially.
In order to monitor an exhaust gas cleaning component for which no coating is provided with an oxygen storage capacity from the outset, it is possible to provide the latter locally with such a coating in a comparatively small, delimited region. Evaluating the increase in temperature which occurs in this region and which is associated with the storage of oxygen therefore permits monitoring and diagnostics to be carried out even on components which are largely free of a coating with an oxygen storage capacity. In this respect it is advantageous to embody the exhaust gas cleaning component in accordance with the variants illustrated in FIGS. 2, 4 and 5.
In order to record the reaction heat of the change in the modification process which occurs when oxygen is stored in the material with an oxygen storage capacity, a temperature sensor is preferably placed in a heat-conducting connection with the corresponding coating. The temperature sensor is preferably introduced into the exhaust gas cleaning component in the radial or axial direction and with its temperature-sensitive region in heat-transmitting contact with the OSC-rich coating.
FIG. 6 is a schematic view of a radial feed of a temperature sensor 7 into an exhaust gas cleaning component 1. The temperature-sensitive region of the temperature sensor 7 can be arranged off-center here; and it of course also possible to position it approximately at the level of the longitudinal central axis.
FIG. 7 is a schematic view of an axial feed of a temperature sensor 7 into an exhaust gas cleaning component 1. It is not necessary for the temperature sensor 7 to be positioned at the level of the longitudinal central axis as illustrated. The sensor axis can be displaced parallel to the longitudinal central axis, intersect it or be at an angle to it.
In exhaust gas cleaning components which, for functional reasons, are made largely free of a coating with an oxygen storage capacity or are made with a coating with a low oxygen storage capacity, it is possible to provide an OSC-rich coating which is provided only in the direct vicinity of the temperature sensor or its temperature-sensitive region. Exemplary embodiments of radial forms of feed for the temperature sensor are illustrated in section in FIGS. 8 a to 8 d corresponding to the sectional lines A and B indicated in FIG. 6. In FIGS. 8 a and 8 c, a region 5, which extends over the entire length of the exhaust gas cleaning component 1 but only part of the cross section and into which the temperature sensor 7 dips, is provided with an OSC-rich coating. In FIG. 8 a, the latter surrounds the temperature-sensitive part of the temperature sensor 7, here its tip, and extends as far as the outer surface of the exhaust gas cleaning component 1. In FIG. 8 c, the OSC-rich region 5 only surrounds the temperature-sensitive region of the temperature sensor 7 in the radial direction. However, according to FIGS. 8 b and 8 d the OSC-rich region 5 is preferably made comparatively short in the axial direction and is only present in the surroundings of the temperature sensor 7.
In FIG. 8 b, the OSC-rich region 5 surrounds the entire sensor 7 from its entry point into the exhaust gas cleaning component 1, and in FIG. 8 d the OSC-rich region 5 surrounds only the temperature-sensitive tip of the temperature sensor 7. With the embodiments illustrated in FIGS. 8 a to 8 d it is therefore possible to monitor for aging of components even on exhaust gas cleaning components which have a coating with little or no oxygen storage capacity.
As illustrated in FIGS. 9 a to 9 c, it is, in an analogous fashion, also possible to introduce a temperature sensor 7 (for example, a thermoelement) axially into the exhaust gas cleaning component 1 which is to be monitored. Temperature sensor 7 may be in heat-transmitting contact with an OSC-rich coating which is formed uniformly over the entire length of the component or in an axial region or, as illustrated, said temperature sensor 7 may be in heat-transmitting contact with an OSC-rich coating which is present only in the direct vicinity of the temperature-sensitive region of said temperature sensor 7.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

1.-9. (canceled)

10. A component for cleaning the exhaust gas in an internal combustion engine, said component comprising:

a carrier body; and

a plurality of flow ducts which pass through the carrier body for accommodating an exhaust gas flow; wherein,

at least some of the walls of the flow ducts have a coating with an oxygen storage capacity;

the coating with an oxygen storage capacity is provided in a first delimited region of the carrier body; and

a second delimited region of the carrier body has no coating with an oxygen storage capacity or has a coating with a greatly reduced oxygen storage capacity, relative to oxygen storage capacity in the first region.

11. The exhaust gas cleaning component as claimed in claim 10, wherein at least one of the first region and second region extends over an entire cross section of the carrier body, and is limited in the axial direction with respect to the extent of the carrier body.

12. The exhaust gas cleaning component as claimed in claim 10, wherein the first region adjoins the second region.

13. The exhaust gas cleaning component as claimed in claim 10, wherein the first region extends over more than half the length of the carrier body.

14. The exhaust gas cleaning component as claimed in claim 10, wherein the first region extends from a point which is spaced apart from an inlet end of the carrier body in an axial direction, to an outlet end of the carrier body.

15. The exhaust gas cleaning component as claimed in claim 10, wherein at least two first regions which are spaced apart from one another are provided.

16. The exhaust gas cleaning component as claimed in claim 10, wherein the exhaust gas cleaning component comprises an exhaust gas catalytic converter.

17. The exhaust gas cleaning component as claimed in claim 10, wherein the exhaust gas cleaning component comprises exhaust gas particle filter.

18. The exhaust gas cleaning component as claimed in claim 10, further comprising a temperature recording device for recording a temperature of the coating with an oxygen storage capacity in the first region.